The sputter deposition of insulating films, particularly Aluminum Oxide (Al.sub.2 O.sub.3), is conventionally accomplished by radio frequency ("RF") diode sputtering from a ceramic target. While somewhat effective, the RF diode sputtering process is quite slow with deposition rates of approximately 500 Angstroms/Minute. With such low deposition rates batch loading is required for economic machine throughput.
Batch processing involves coating multiple substrates in a single deposition run. However, batch processing has long been recognized by the semiconductor industry as less than optimum because of several factors. First, batch processing requires the use of larger targets, and thus much greater (and more expensive) power supplies are required. Second, there is an increased risk that wafer-to-wafer deposition uniformity will vary. Third, if there is a problem during a deposition run, multiple wafers will be lost. Thus, with batch processing, greater compromises must be made to distribute process results over the batch.
Single substrate processing, on the other hand, offers the benefits of better wafer-to-wafer deposition control and reduced losses in non-useable wafers due to deposition run problems. However, a commercially viable deposition rate would have to be increased by a substantial amount over the rate achievable in conventional RF diode sputtering systems. For example, a three times increase in deposition rate over the conventional RF diode approach would yield an acceptable rate for commercial applications. This increased rate can be achievable by utilizing a reactive sputtering process. In one reactive sputtering technique, an Aluminum target is placed in proximity to the presence of Oxygen to create an Al.sub.2 O.sub.3 film as it is being deposited. The rate increase is realized because the sputter rate for metallic Aluminum is many times faster than for Aluminum Oxide and more conventional DC type power supplies can be used.
In addition to deposition rate, another important processing parameter is the deposition uniformity, which directly impacts the number of usable devices yielded from each substrate. An acceptable commercial deposition full range uniformity (of the coating layer thickness over the entire substrate) is &lt;2% and is thus a major parameter in the source design. To achieve this kind of uniformity a large area sputter target would be needed.
To realize increased deposition rates for depositing metal films, conventional "magnetron" designs have been developed. These magnetron systems typically include a source, a metal target (typically Aluminum (Al) acting as a cathode), an electrode, and a substrate in close proximity to the electrode. A sputter gas medium, such as Argon (Ar) is introduced in the vacuum chamber and is ionized. The Ar.sup.+ ions accelerate towards the negatively charged target and collide with the target to release Al atoms that are deposited on the substrate.
One conventional magnetron design utilizes a stationary magnet to generate a magnetic field that is used to keep electrons from escaping the target vicinity before ionizing a number of Ar atoms which sputter the target. However, use of stationary magnets creates a "trenching" of the target which results in a non-uniform erosion of the target. This is disadvantageous because utilizing a non-uniform erosion pattern increases the risk that the deposited film will be non-uniform.
Other conventional sputter source designs include a rotating magnet to provide both high rate and large area coverage. These rotating magnet designs are typically offset (and are thus asymmetrical) with respect to the rotating axis and come in a variety of shapes, such as heart-shaped (cartioid) and apple-shaped rotating magnets. Examples of such magnet designs are provided in U.S. Pat. Nos. 4,995,958; 5,194,131; and 5,248,402. However, these conventional rotating magnet designs were developed almost exclusively for metal film deposition, and as such were not ideally suited for reactive sputtering.
Thus, what is needed is a magnet design, sputtering source and process that provides an acceptable quality film (in terms of film uniformity) on a substrate, where the deposition rate is sufficiently fast to allow single substrate processing (as opposed to batch processing) in order to eliminate the time and control problems stemming from the repeated venting of the substrate chamber under the conventional batch processing technique. Automated handling with a single substrate processing technique is desirable for its reduction in processing time, as well as providing for process control benefits.